This application is a 371 of PCT/JP99/04467 filed Aug. 20, 1999.
The present invention relates to a radio communication terminal apparatus for use in a radio communication system such as a cellular phone, a car phone, etc., and relates to a transmission power control method.
In order to perform favorable communications in a radio communication system such as a cellular phone, a car phone, etc., which have proliferated in recent years, precise control of transmission power is an absolute necessity for a base station apparatus and a radio communication terminal apparatus (hereinafter simply referred to as xe2x80x9cterminal apparatusxe2x80x9d).
The following will explain the action of a conventional terminal apparatus with reference to the drawing. FIG. 1 is a block diagram showing a configuration of the conventional terminal apparatus.
A signal received by an antenna 11 is input to a reception RF section 13 via a duplexer 12, power of the received signal is amplified, and the frequency of the received signal is converted, and a baseband signal is extracted. This baseband signal is demodulated by a demodulating section 14, and an individual channel signal of the terminal apparatus is picked up.
Also, reception power of the individual channel of the terminal apparatus output from the demodulating section 14 is measured by a reception power measuring section 15, and a gain of a transmission amplifier is calculated by a transmission power control section 15 based on the reception power.
A transmission signal is modulated by a modulating section 17, and the frequency thereof is converted by a transmission RF section 18, and power thereof is amplified based on the gain of the transmission amplifier, and the resultant is transmitted from the antenna 11 via the duplexer 12.
Here, it is required that the communication apparatus controls transmission power in consideration an amount of attenuation such that the radio transmitted signal is attenuated at a propagation path. The terminal apparatus controls transmission power such that reception power becomes constant in the base station apparatus.
At time t1, it is assumed that the gain of the transmission amplifier of the base station apparatus is set to GB(t1) and that an amount of attenuation of a forward link is set to LD(t1). Reception power RM(t1) of the individual channel received by the terminal apparatus can be calculated by equation (1) shown below.
Also, at time t2, it is assumed that the gain of the transmission amplifier of the terminal apparatus is set to GM(t2) and that an amount of attenuation of a reverse link is set to LU(t2). Reception power RB(t2) of the base station apparatus can be calculated by equation (2) shown below. In this case, the respective power values explained below are unified by an expression dB and calculated by addition and subtraction since they treat the gain.
RM(t1)=GB(t1)xe2x88x92LD(t1)xe2x80x83xe2x80x83(1)
RB(t2)=GM(t2)xe2x88x92LU(t2)xe2x80x83xe2x80x83(2)
Here, in a TDD (Time Division Duplex) communication system, since the same frequency is used in the reverse link and the forward link, if a time distance between a reception slot and a transmission slot is short, the propagation paths of these slots can be regarded as the same. Then, the amount of attenuation LD(t1) of the forward link at time t1 and that of attenuation LU(t2) of the reverse link at time t2 can be treated as the same.
Therefore, the gain GM(t2) of the transmission amplifier of the terminal apparatus results in a value, which is obtained by adding the amount of attenuation LD(t1) of the forward link to the reception power RB (t2) of the base station apparatus, which is a predicted target gain, and this can be expressed by equation (3) shown below.
GM(t2)=RB(t2)+LD(t1)xe2x80x83xe2x80x83(3)
Here, in a case where the gain GM(t1) of the transmission amplifier of the base station apparatus is constant and the predictive reception power RB(t2) of the base station apparatus is constantly controlled, it is assumed that these added values are set to a fixed gain G0. In this case, GM(t2) of the transmission amplifier of the terminal apparatus can be calculated from equations (1) and (3) by equation (4) shown below.
GM(t2)=G0xe2x88x92RM(t1)xe2x80x83xe2x80x83(4)
Thus, the conventional terminal apparatus controls the gain GM(t2) of the transmission amplifier such that the reception power RB(t2) of the base station apparatus becomes constant on the basis of the measured reception power RM(t1).
Here, in a case where the base station apparatus transmits the signal with a narrow directivity, the reception power is lowered by the directional shift with respect to the terminal apparatus in addition to the attenuation of reception power at the propagation path.
In this case, even if the received signal is lowered by the directional shift, the aforementioned conventional terminal apparatus determines as attenuation at the propagation path and transmits the signal with an excessive power, and this causes problems wherein an amount of interference to the other peripheral terminal apparatuses increases to make it impossible to perform communications with the other peripheral terminal apparatuses and a battery lifetime shortens.
It is an object of the present invention is to provide a terminal apparatus, which can correctly determine the cause of a reduction in reception power and control transmission power precisely, and to provide a transmission power control method.
The above object can be attained by calculating a transmission gain from reception power of individual channels, determining the presence or absence of a directional shift from a ratio between an average reception power of individual channels and an average reception power of common channels, and calculating a correction value in the case of the presence of the direction shift, whereby correcting the transmission gain.